This invention relates to the analysis of centrifuged anticoagulated blood samples which are contained in a centrifuge tube having a blood constituent-elongating insert therein. More particularly, this invention relates to a centrifuge tube assembly which is useful for measuring various blood parameters such as hematocrit, and which is also designed to examine the blood sample for evidence of rare events such as: blood-borne cancer cells; malarial parasites; other hemato-parasites; bacteria; or the like. The blood sample can also be analyzed in the tube for hematocrit and hemoglobin values as well as white cell and platelet counts.
U.S. Pat. No. 4,027,660 granted to Stephen C. Wardlaw et al describes a method and paraphernalia for use in measuring differential white cell and platelet counts in a centrifuged sample of anticoagulated whole blood. The procedure described in this patent suggests that a scale be used to measure the length of physically expanded white cell and platelet layers, and that a table be used to convert the measured layer lengths to definitive blood cell and platelet layer counts. U.S. Pat. Nos. 4,156,570 and 4,558,947 granted to Stephen C. Wardlaw disclose instruments which are used to measure cell and platelet counts in centrifugal blood samples contained in the aforesaid tube-insert paraphernalia, which instruments include microprocessor controllers that are programmed to automatically convert measured erythrocyte and platelet layer band lengths into cell and platelet counts. U.S. Pat. No. 4,259,012 granted to Stephen C. Wardlaw, and U.S. Pat. No. 5,132,087 granted to Kristen L. Manion et al describe devices for measuring white cell, platelet and hematocrit counts, which devices do not require conversion tables or microprocessor controllers. U.S. Pat. No. 4,209,226 granted to Stephen C. Wardlaw et al describes an optical viewing instrument which includes a capillary tube and a holder which includes a slot for containing the capillary tube. U.S. Pat. No. 4,190,328 granted to Robert A. Levine et al describes a process for the detection of blood-borne parasites wherein a centrifuge tube with an insert are used to trap blood-borne parasites between the tube and the insert so that the parasites will be visible under magnification through the tube.
The aforesaid group of patents all relate to inventions which utilize a tube and insert combination to either measure blood sample parameters quantitatively; or detect the presence or absence of blood-borne parasites, such as malarial parasites, microfilaria, or the like. In the latter case, the blood samples in the tubes are examined immersed in oil and under magnification, typically with an epi-illuminating UV or fluorescence microscope such as described in U.S. Pat. No. 5,198,927, granted Mar. 30, 1993 to R. R. Rathbone et al; and U.S. Pat. No. 5,349,468, granted Sep. 20, 1994 to R. R. Rathbone et al. When the centrifuged blood sample is being analyzed for parasites, or for blood borne rare events, there is currently no way to positively ascertain the location of the evidence of rare events in the centrifuge tube. The reason for this fact is that analysis of the blood sample in the tubes requires that the tubes be rotated so that the blood layers trapped between the tube wall and the insert can be thoroughly examined throughout the entire three hundred sixty degree circumference of the tube.
Present closures of capillary tubes are of three different varieties: simple clay, which is pressed into the tube from a tray; an internal closure described in U.S. Pat. No. 5,325,977 granted Jul. 5, 1994 to J. L. Haynes et al; and caps of the type shown in U.S. Pat. No. 5,132,087, granted Jul. 21, 1992 to K. L. Manion et al, and also shown in other issued patents.
To accurately measure the hematocrit height one must be able to accurately locate the lower and upper end of the packed erythrocyte layer. To examine centrifuged samples of blood for rare events, one must be able to position the objective of a microscope proximate the tube. The degree of sample magnification needed to examine the sample for rare events is generally 50xc3x97. Microscopic examination of the sample generally requires the use of an oil immersion for the tube on the microscope stage, and an objective lens which has a working distance of at least one hundred sixty microns. During the sample examination, the objective lens of the microscope must be disposed closely adjacent to the surface of the tube, or even touching the tube through the oil layer.
During microscopic examination of the sample, the tube must be manually rotated about its axis using one""s fingers so as to be able to examine the entire circumference of the tube in the areas of interest. The areas in the blood sample which are of interest for rare events can include the areas in the blood sample which surround the portions of the insert which are submerged in the erythrocyte layer, and which are surrounded by both erythrocytes, buffy coat components, and, in some ases, by plasma at the upper end of the insert.
Closures of the aforesaid first and second types, while permitting accurate detection of the lower and upper ends of the erythrocyte layer, and permitting the the oil-immersed microscope objective to contact the capillary tube, do not facilitate accurate rotation of the oily tube and closure. The reason for this is that the glass tube and closure are smooth , and are frequently covered with oil thereby rendering the tube assembly extremely difficult to rotate when rotational pressure is manually applied with one""s fingers. Furthermore, if manual pressure is applied to the tube assembly, the tube might fracture, thereby destroying the sample and potentially injuring the technician.
Closure caps of the third type described above, while not impeding manual rotation of the tube by means of manual contact with the cap, do render detection of the lower end of the erythrocytes difficult because the lower end of the erythrocyte layer will be obscured by such closure caps. A person with severe anemia, or one experiencing abdominal bleeding, can have a hematocrit of about twenty or less. In cases of such low hematocrits, i.e., hematocrits which are below levels of about twenty, the upper end of the packed erythrocytes may be positioned at or near at the upper edge of the cap, thereby rendering the upper end of the packed erythrocyte layer difficult to detect and obscured by the closure cap. Thus, when using closure caps of the aforesaid third type, hematocrit measurement may be difficult, or impossible to perform.
When microscopical rare event examination is attempted of the centrifuged blood sample in a tube-and-insert assembly that utilizes the aforesaid third type of closure, one may be unable to position the objective lens set of the microscope sufficiently close to the sample tube to examine appropriate portions of the centrifuged sample due to mechanical interference between the microscope""s objective lens set and the tube assembly closure cap. Thus, in all centrifuged blood samples which are contained in an assembly that employs the aforesaid third type of closure cap, at least a portion of the expanded portion of the erythrocyte layer which surrounds the float cannot be examined under a microscope for rare events, and in a blood sample with a hematocrit of less than about twenty, none of the expanded portion of the erythrocyte layer which surrounds the float can be examined under a microscope for rare events. Thus, while the third type of closure cap may allow manual rotation of an oily sample tube assembly, such a sample tube assembly limits the ability to microscopally examine the expanded portion of the erythrocyte layer which surrounds the float for the presence or absence of rare events.
The problem which is encountered in the examination of the blood samples for hematocrit relates to the fact that the closures of the third type entrap a significant portion of the erythrocytes, thereby lowering the upper end of the erythrocyte layer, and obscuring the entrapped erythrocytes from a hematocrit scale or optical sensors. This problem prevents hematocrits of less than about twenty from being accurately measured. It will be noted that the hematocrit scale shown in the aforesaid U.S. Pat. No. 5,132,087 patent only goes down to twenty. Thus, critical hematocrit values are not readable with this prior art equipment.
It would be desirable to be able to examine a centrifuged anticoagulated whole blood sample for evidence of blood borne rare events, such as circulating cancer cells, malarial parasites, microfilaria, bacteria, and the like, with equipment which allows the investigator to microscopally examine essentially the entire erythrocyte column for evidence of rare events, and accurately record the location of any noted rare event evidence in the sample holder; and also obtain accurate hematocrit, hemoglobin, and blood constituent count values from the blood sample in the same sample tube.
This invention relates to a system which can be used to examine a centrifuged sample of anticoagulated whole blood for rare events, microfilaria, and can also be used in the measurement of hematocrit values in the centrifuged blood sample. The system of this invention includes a transparent sample tube, which may be a capillary tube, an insert which resides in the tube in the manner described in the above-identified prior patents. The insert floats in the packed erythrocyte layer in the centrifuged blood sample, and vertically or longitudinally expands all of the cell layers which surround the insert or float. The insert also forces any evidence of rare events to the periphery of the blood sample in the tube where it can be detected through the tube wall.
The bottom end of the tube is closed by means of a cap which includes an inner plug that extends up into the tube bore to an extent necessary to ensure that the entire centrifuged erythrocyte layer will be visible in the tube above the cap when the blood sample is centrifuged. The tube closure cap also includes an outer tube-engaging sheath having annular surface which is provided with differentiated sensible indicia, such as numbers or letters, or the like. The indicia can be embossed or debossed, or otherwise placed on the surface of the closure cap, and are evenly spaced about the annular surface so that one examining the sample can determine the circumferential location in the tube of any suspicious objects noted in the blood sample. The microscope stage can also be equipped with an axial movement-measuring micrometer so that the axial position in the tube of any rare event evidence noted in the blood sample can also be determined and recorded. The assembly can thus be used to enable the determination of both the axial and circumferential coordinates of each piece of rare event evidence noted in the blood sample. The indicia, when raised on the annular surface, impart increased friction to the closure cap so that the tube can be more easily manually rotated on a microscope slide despite the tube assembly""s tube and cap being slippery as a result of being immersed in oil.
The outer sheath of the closure cap could, instead or additionally, be provided with molded gear teeth which would include a sensible reference tooth, or other sensible structure, that would enable the tube to be manually or mechanically rotated from the same start point each time the tube is inserted into a reading instrument. A complementary rotating gear could be provided in the reading instrument, which rotating gear can be controlled by an instrument controller processor, or the rotating gear could be manually-actuated. Thus, the closure cap with its raised indicia and/or molded gear teeth will enable one to visually record the location of rare event evidence, or to instrumentally record the location of any rare event evidence found in the blood sample, and would also allow one to selectively rotate the tube to a new field of view which is to be inspected.
It is therefore an object of this invention to provide an improved assembly for examining a sample of centrifuged anticoagulated blood for blood borne evidence of physiological rare events.
It is a further object of this invention to provide an assembly of the character described which includes a transparent sample tube containing a volume-occupying insert and having a basal closure cap.
It is an additional object of this invention to provide an assembly of the character described wherein the closure cap is provided with an internal plug which extends into the tube and provides a surface for centrifuged erythrocytes to settle onto to a degree wherein virtually the entire erythrocyte layer will be visible through the tube.
It is yet an additional object of this invention to provide an assembly of the character described wherein the internal plug extends into the tube sufficiently so as to locate the lowest end of the erythrocyte layer in a position within the tube that is sufficiently offset from the remainder of the closure cap so that the objective lens set of a microscope can be positioned relative to the tube so that the microscope can be focused on the portion of the erythrocyte layer which surrounds the insert in the tube.
It is another object of this invention to provide an assembly of the character described wherein the closure cap is provided with an external annular sheath having an outer surface that has differentiated sensible indicia thereon for the purpose of identifying the rotational position of the tube and sample.
It is yet another object of this invention to provide an assembly of the character described wherein the external annular sheath has an outer surface that is roughened for the purpose of facilitating rotation of the tube and sample while the tube is positioned in an examining instrument.
These and other objects and advantages of the invention will become more readily apparent from the following detailed description of several embodiments of the invention when taken in conjunction with the accompanying drawings in which: